Use this dialog box to specify details for the islands located in the approach roads of the roundabout.
This dialog box is the third in a series of four dialog boxes that step you through creating a roundabout. It lets you configure geometry parameters for the construction triangle and splitter island in each approach road of the roundabout.
Approach Road Alignments Selected
The number of approach road alignments that are currently selected for creating this roundabout is displayed at the top of this dialog box.
- Previous\Next
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Use these buttons to scroll through and specify parameters for islands included in each of the approach roads. If you want to apply the same parameters to all of the approach roads, use the Apply To All button. If you want to apply different parameters for the approach roads, do not use the Apply To All button.
The approach road alignments are named using a naming convention that identifies the direction of the base alignment that was selected; for example, an “East to west approach” road contains “EW” in the approach road alignment name (Approach_EW_).
- Apply to All
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Clicking this button applies the parameters that are currently specified on this dialog box to all of the approach roads included in this roundabout.
Predefined Parameters To Import
You can select a set of parameters from the dropdown list. As soon as you select a set of parameters, the Entry, Exit, Construction Triangle and Splitter Island Parameters are updated with the selected values. If desired, you can change the value of any parameter.
To add a new set of parameters to the list, click 
. The Preset - Add dialog box is displayed.
Enter a preset name for the new set of parameters, and then enter the values for all parameters. If you want to edit existing sets of predefined parameters, select the preset that you want to edit from the list of presets and click 
. To erase an existing set of predefined parameters, select the preset that you want to erase from the list of presets and click 
.
Construction Triangle Parameters
These parameters specify the geometry of the construction triangle in the islands included in the roundabout.
Hovering the cursor over these controls displays a conceptual illustration of the component or geometry specified by that control on the right side of this dialog box.
- Length
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Specifies the length of the construction triangle.
- Base
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Specifies the width of the construction triangle base.
- Base Offset
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When the French (SETRA) roundabout drawing standard is selected, this parameter is displayed to specify the offset of the base from the central alignment. If your base offset is half of the base value, then the central alignment will go through the midpoint of the construction triangle base.
- Tip Offset
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When the French (SETRA) roundabout drawing standard is selected, this parameter is displayed to specify the offset of tip of the construction triangle from the central alignment. If you use the value “0”, then the tip of the construction triangle will be exactly on the central alignment.
Splitter Island Parameters (US Imperial)
These parameters specify the geometry of the splitter island included in the roundabout.
These parameters are displayed only when the US_Imperial roundabout drawing standard is selected on the Create Roundabout - Circulatory Road dialog box.
Hovering the cursor over these controls displays a conceptual illustration of the component or geometry specified by that control on the right side of this dialog box.
- Provide Crosswalk (Length)
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Selecting this option divides the splitter island to accommodate a crosswalk. When this option is selected, the Length and Island Base Length parameters are displayed.
- Length
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When the Provide Crosswalk option is selected, the Length option are displayed. This specifies the length of the crosswalk being added to the splitter island.
- Island Total Base
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When the Provide Crosswalk option is selected, this option is displayed. It specifies the length of the splitter island from the base to the crosswalk.
- Island Total Length
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Specifies the length of the splitter island from its tip to its base.
- Rounding At Exit
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Specifies the rounding of the splitter island at the exit.
- Offset From Circle At Exit
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Specifies the offset of the splitter island from the circulatory area at the exit.
- Offset At Exit
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Specifies the offset from the splitter island on the exit lane at the base of the construction triangle.
- Offset At Departure
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Specifies the offset from the splitter island on the exit lane at the tip of the construction triangle.
- Rounding At Tip
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Specifies the rounding of the splitter island at the tip.
- Rounding At Entry
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Specifies the rounding of the splitter island at the entry.
- Offset From Circle At Entry
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Specifies the offset of the splitter island from the circulatory area at the entry.
- Offset At Entry
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Specifies the offset from the splitter island on the entry lane at the base of the construction triangle.
- Offset At Approach
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Specifies the offset from the splitter island on the entry lane at the tip of the construction triangle.
- Rounding At Crosswalk
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Specifies the rounding of the splitter island at the crosswalk.
Splitter Island Parameters (French)
The following parameters are displayed when the French (SETRA) roundabout drawing standard is selected on the Create Roundabout - Circulatory Road dialog box.
- Radius At Curbs
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Specifies the radius of the splitter island fillets at all three corners.
- Base Offset
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Specifies the offset of the splitter island to the base of the construction triangle.
- Side Offset
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Specifies the offset of the splitter island to the left and right side of the construction triangle.